<!doctype html>
<html lang="en">
 <head>
  <meta charset="UTF-8">
  <meta name="Generator" content="EditPlus®">
  <meta name="Author" content="">
  <meta name="Keywords" content="">
  <meta name="Description" content="">
  <title>Document</title>
  <script>
      var arr = ["学习练习/img/img_14.jpg","学习练习/img/img_15.jpg","学习练习/img/img_16.png"];
      var n = 0;
      function show1(){
	    var img = document.getElementById("img");
	    switch(n){
		 case 0:
		    n = 2; img.src = arr[n]; break;
		 case 1:
		    n = 0; img.src = arr[n]; break;
		 case 2:
            n = 1; img.src = arr[n]; break;
		}
	  }
	  function show2(){
		var img = document.getElementById("img");
	    switch(n){
		 case 0:
		    n = 1; img.src = arr[n]; break;
		 case 1:
            n = 2; img.src = arr[n]; break;
		 case 2:
			n = 0; img.src = arr[n]; break;
		}
	  }
  </script>
  <style>
    div{
	  width:200px;
	  height:200px;
	  border:solid 1px black;
	}
	img{
	   width:200px;
	   height:200px;
	}
  </style>
 </head>
 <body>
   <div>
     <img src="学习练习/img/img_14.jpg" id="img">
   </div>
   <button onclick="show1()">上一张</button><button onclick="show2()">下一张</button>
 </body>
</html>
